The present invention relates generally to a processing method for use with a semiconductor exposure apparatus and the like, and more particularly to environmental control over a load lock chamber that replaces an atmosphere between the air and a reduced pressure or vacuum atmosphere.
The developed exposure technology using synchrotron radiations has recently been sought for finer processing in the semiconductor fabrication, but the synchrotron radiation has a problem of X-ray attenuations in the air. Accordingly, a conventional processing system as one solution for this problem houses principal part of an exposure apparatus in a helium purged process chamber that reduces X-ray attenuations.
This processing system typically includes a load lock chamber that delivers a wafer between a port as a supply part and the process chamber, and exchanges its atmosphere between the air and the reduced pressure or vacuum atmosphere. The load lock chamber includes gate valves between the load lock chamber the port and between the load lock chamber and the process chamber. The gate value between the load lock chamber and the process chamber closes when the wafer is delivered between the port and the load lock chamber, and the load lock chamber is maintained at an the ambient pressure. The gate valve between the load lock chamber and the port closes when the wafer is delivered between the process chamber and the load lock chamber, and the load lock chamber is maintained at the reduced pressure or vacuum atmosphere.
Every wafer is subject to an atmosphere conversion from the air to helium in the load lock chamber, and then delivered to and exposed in the process chamber. It is returned to the load lock chamber after exposure, subject to an atmosphere conversion from helium to the air in the load lock chamber before taken out.
Before the atmosphere of the load lock chamber is replaced with helium, the load lock chamber should be vacuum-pumped once and then filled with helium at the same pressure as the process chamber to maintain the helium purity in the process chamber when the wafer is delivered to the process chamber. In returning the load lock chamber to the ambient pressure to take out the exposed water, the load lock chamber is vacuum-pumped and then filled with nitrogen or purifying air at the ambient pressure when helium is recovered, purified and recycled.
Thus, while the load lock chamber is being vacuum-pumped, an abrupt pressure drop results in adiabatic cooling, lowers the saturated moisture pressure, and forms dew when the load lock chamber is wet. For example, when the temperature of gas with the humidity of 50% drops down to about 12° C., the humidity becomes 100% and forms dew. There have been proposed some anti-condensation means for decontaminating a wafer, such as a method for slowing down the vacuum pumping speed, a method for introducing hot gas before vacuum pumping in order to compensate temperature that has dropped due to the adiabatic cooling (e.g. Japanese Patent publication No. 2000-40669), and a method for heating the inside of the load lock chamber.
However, a slow vacuum-pumping speed of the load lock chamber would disadvantageously lower the throughput in the exposure apparatus. An introduction of the hot gas and heating of the load lock chamber before vacuum pumping would transmit the undesirable heat to the temperature-controlled process chamber and harm its temperature stability, lowering the yield of the exposure apparatus.